The present disclosure relates to an optical information recording medium. More specifically, the present disclosure relates to an optical information recording medium having two or more information signal layers.
Hitherto, CDs (Compact Discs) and DVDs (Digital Versatile Discs) and the like have driven the market for optical information recording media. However, in recent years, there has been a demand for optical information recording media with a further increased capacity accompanying a rapid increase in data handled by high definition televisions and PCs (Personal Computers). Mass storage optical information recording media for blue lasers such as BD (Blu-ray Disc (registered trademark)) have been developed to meet such a demand and the market for new, mass storage optical information recording media is continuing to grow.
As recordable optical information recording media, there are rewritable optical information recording media as represented by CD-RW (Compact Disc-ReWritable), and DVD±RW (Digital Versatile Disc±ReWritable), as well as write-once optical information recording media as represented by CD-R (Compact Disc-Recordable), and DVD-R (Digital Versatile Disc-Recordable). In particular, the latter have contributed greatly to the expansion of the market as low cost media. Accordingly, with large capacity optical information recording media for blue lasers as well, it is necessary to lower the price of write-once optical information recording media in order to expand the market. Furthermore, it is generally said that the storage reliability of the optical information recording media is high compared to hard disk drives (HDD), flash memory and the like due to the recording and reproduction principles thereof, with the result that in recent years such media have been in more and more demand as archival media such as those which are beginning to be used to store important information.
As the recording material used in write-once optical information recording media, there are inorganic material and organic coloring material. In a typical write-once optical information recording medium, organic coloring materials have been primarily studied as the recording material. However, in the large-capacity optical information recording media of recent years, inorganic materials have been studied extensively as the recording material.
For example, in Japanese Unexamined Patent Application Publication No. 2010-218636, an optical information recording medium having an inorganic recording layer including Pd and O is proposed. In addition, in a similar optical information recording medium in Japanese Unexamined Patent Application Publication No. 2009-129526, an optical information recording medium, which is provided with a protective layer of a mixture (ITO) of indium oxide and tin oxide as a main component on at least one surface of the inorganic recording layer including Pd and O in order to achieve both storage reliability and good productivity, is proposed.